1. Field of the Invention
The present invention relates to a hydraulic circuit system for hydraulic working machine such as a hydraulic excavator, and more particularly to a hydraulic circuit system for hydraulic working machine in which the maximum of predetermined ones of operation signal pressures generated by a plurality of pilot operating units is detected by shuttle valves, and the detected maximum pressure is used as a control signal pressure to operate a control device such as a regulator for a hydraulic pump.
2. Description of the Prior Art
JP, B2, 2534897 and JP, A, 3-144024 disclose examples of a hydraulic circuit system in which the maximum of predetermined ones of operation signal pressures generated by a plurality of pilot operating units is detected by shuttle valves, and the detected maximum pressure is used as a control signal pressure to operate a control device.
FIG. 21 shows the hydraulic circuit system disclosed in JP, B2, 2534897. The disclosed hydraulic circuit system includes, as the control device operated by the control signal pressure, a regulator for controlling a tilting of a hydraulic pump.
More specifically, in FIG. 21, a hydraulic fluid delivered from a variable displacement hydraulic pump 101 is supplied to and returned from actuators 105, 106, 107 through flow control valves 102, 103, 104, respectively. Pilot operating units 108, 109, 110 are provided for the actuators 105, 106, 107, respectively. The pilot operating units 108, 109, 110 include pilot valves (pressure reducing valves) built therein, and generate operation signal pressures from the pressure of a pilot pump 100 depending on the direction and input amount in and by which respective control levers are manipulated, the operation signal pressures being supplied so as to act on the corresponding flow control valves 102, 103, 104. The maximum of the operation signal pressures generated by the pilot operating units 108, 109, 110 is detected by shuttle valves 111, 112, 113, 114 and 115. The detected maximum pressure is transmitted as a control signal pressure to a regulator 116 for the hydraulic pump 101. The regulator 116 is thereby operated to control a tilting, i.e., a delivery capacity, of the hydraulic pump 101.
Further, the hydraulic circuit system disclosed in JP, A, 3-144024 includes a merging/branching circuit selector valve for two hydraulic pumps which is a control device operated by a control signal pressure, and two valve blocks, i.e., a shuttle valve block and a pilot selector valve block, which serve as means for extracting, as the control signal pressure, the maximum in a group of operation signal pressures. The shuttle valve block detects the maximum for each of a plurality of operation signal pressure groups selected from among from the operation signal pressures generated by a plurality of pilot operating units, the detected maximum pressures being introduced to the pilot selector valve block. The pilot selector valve block extracts one of the maximum pressures selected by the shuttle valve block with a combination of shuttle valves and pilot selector valves which are provided in the pilot selector valve block. The extracted maximum pressure is introduced, as the control signal pressure, to the merging/branching circuit selector valve, whereupon the merging/branching circuit selector valve is shifted.